The present invention relates generally to electric motors and, more particularly, to a two compartment electric motor and a method of manufacturing a two compartment electric motor.
Single phase induction motors are manufactured in a variety of types and configurations. In addition to the stator, armature and other primary motor compartments, some types and configurations include electrical or electronic components which are used to modify operating characteristics for particular applications. Examples of such motors are resistance start, reactor start, capacitor start, permanent split capacitor, and capacitor start-capacitor run motors. These different types of motors are characterized by different speed-torque characteristics, and may be designed to provide different theoretical maximum efficiencies. For some applications, particularly those where high starting torque is required, part of the windings in a motor may be designed and arranged to serve as auxiliary or starting windings which are energized during initial excitation of the motor, but which are deenergized as the motor comes up to a predetermined speed. Deenergization of such windings is often accomplished by a centrifugal switch, or other appropriate device.
In some applications, and especially those applications of motors used to drive pumps such as jet pumps or swimming pool pumps, capacitors, circuit controlling switches (e.g., speed control switches, voltage control switches, overload devices, etc.), and other electrical components are mounted to one of the motor end frames to facilitate access thereto. To provide protection from moisture, dust and other contaminants, such components are often mounted in a closed "control compartment" which is disposed immediately adjacent the "motor compartment" which houses the armature and other primary motor components.
U.S. Pat. No. 4,593,163, which is commonly assigned to the assignee of the present invention, discloses a two compartment motor in which components such as a starting capacitor, a thermal protector, a terminal board and motor circuit controlling switch assembly (e.g., a starting switch assembly), and a manually actuable switch are mounted to an end shield of an induction motor assembly. A thermoplastic molded cover is fastened to the motor with axially directed mounting screws. The end shield to which the components are mounted and the molded plastic cover define a "control compartment" in which the subject electrical components are housed.
An object of the present invention is to provide an improved two compartment motor design.
Another object of the present invention is to provide a two compartment motor design which may be more easily and reliably manufactured.
Yet another object of the present invention is to provide a two compartment electric motor design which includes a control plate in the control compartment to which a plurality of electrical components may be conveniently mounted.
Yet another object of the present invention is to provide a two compartment motor design in which a plurality of electrical control components may be premounted to a control plate to form a sub-assembly prior to the assembly of the control compartment of the motor.
Still another object of the invention is to provide a two compartment motor with improved ventilation features which may be integrally formed in the control plate.
These and other objects of the invention are achieved in a two compartment motor which comprises a frame, a pair of end shields disposed adjacent opposite ends of the frame to define a first compartment, stator windings supported by the frame within the first compartment, an armature rotatably supported by the end shields and disposed within the first compartment adjacent the stator windings, a cover mounted to the motor adjacent one of the end shields to define a second compartment between the cover and the end shield, and a control assembly mounted within the second compartment. The control assembly comprises a control plate, a plurality of electrical components, and mounting means for securing the electrical components in position on the control plate. In one embodiment of the invention, the control plate is a molded plastic component and the mounting means is integrally formed or molded with the control plate. The electrical components may include a starting capacitor. In this case, the control plate may be formed with opposed, integrally molded, resilient fingers for securing the starting capacitor to the control plate. The components may also include a voltage selection switch, and at least a portion of the switch may be integrally molded with the control plate. Similar switches may be provided for speed selection or other purposes.
The components mounted to the control plate may also include an overload device, and one or more electrical terminals used, for example, as a termination point for electrical conductors supplying power to the motor. In the case of the overload device, the control plate includes integrally formed means, such as one or more openings to receive threaded fasteners, for securing the overload device to the control plate. The control plate may also be provided with a plurality of integrally formed ventilation openings for providing a flow of ventilating air to or from the motor.
In one embodiment of the invention, the armature includes a shaft which extends into the second compartment and through the control plate. An integrally formed shield to guard against unintended contacts between this portion of the shaft and the electrical components and conductors within the second compartment may be provided on the control plate. This embodiment of the motor further comprises a centrifugal switch assembly having a rotatable portion mounted on the shaft. An integrally molded recess for receiving and shielding the rotatable portion of the centrifugal switch assembly is provided on one side of the control plate. An actuator portion of the switch may be mounted by means of integrally formed mounting means to an opposing side of the control plate. An opening in the control plate is provided to allow interaction between the actuator portion of the switch assembly and the rotatable portion to control an electrical circuit.
The control plate may also be provided with a recess for receiving mating electrical conductors which electrically connect the stator windings to one or more of the electrical components in the second compartment. In this embodiment, a first electrical connector is provided and connected by conductors to at least one of the electrical components in the second compartment. This conductor may extend through an opening in the control plate such that the connector is disposed between the control plate and the adjacent end shield. A second connector is provided and is connected by conductors to the stator windings. These conductors extend through an opening in the end shield such that the second connector is also disposed between the control plate and the end shield. The control plate is formed with an integrally molded recess adapted to receiving the mated first and second connectors.
Another aspect of the present invention relates to the end shield which lies adjacent the cover to define the second compartment and which has a "skeleton" construction. This end shield comprises a central portion, a circumferential rim portion, and a plurality of radially extending spokes connecting the central portion to the circumferential rim portion. The end shield is provided with at least one relatively large opening between the central and circumferential rim portions and between adjacent ones of the radially extending spokes to allow for the passage of ventilating air and electrical conductors from the first to the second compartments. The central portion of the end shield comprises a first recess on a first side thereof for receiving an armature supporting bearing therein. A second recess may be provided on a second, opposing side thereof for providing clearance for the rotating portion of the centrifugal switch assembly. The end shield may also be provided with an integrally formed conduit receiving opening. The end shield is preferably formed of a one-piece construction from a material such as cast aluminum. The conduit receiving opening is formed in an upstanding portion of the casting. A step-like shoulder is provided around at least a portion of the conduit opening and is adapted to interact with an edge of the cover to provide a seal to prevent entry of dust, moisture and other contaminants. At least one locating boss may be formed on either the circumferential rim portion or on one of the spokes of the end shield to provide a mechanism for aligning the end shield and the control plate in a preferred relative orientation.
In one embodiment of the invention, the cover comprises a one-piece, molded plastic element. An integrally molded shield may be provided on an interior surface of the cover for shielding an end portion of the rotating shaft of the armature from the electrical components and conductors in the second compartment. The shield comprises a generally arcuately shaped element extending around at least a portion of the rotating shaft. The cover is a cup-shaped element having a peripheral edge formed to abut portions of the control plate and the adjacent end shield so as to effectively define the second compartment and shield the electrical components from view and contamination.
In one embodiment of the invention, the voltage or speed selection switch, which may be among the plurality of components on the control plate, comprises a movable portion and a stationary portion. The stationary portion is integrally formed in the control plate. This portion comprises at least one electrical terminal mounted in the control plate and adapted for mating with an electrical conductor in the movable portion. In a preferred embodiment of the switch, at least two electrical terminals are mounted in the control plate, and conductor means for electrically connecting the terminals is provided in the movable portion. The switch means has a plurality of engaged positions wherein the movable portion is electrically engaged with the stationary portion, and a disengaged position wherein the movable portion is selectively movable to or between first and second engaged positions. The stationary portion comprises one or more arcuate portions which extend outwardly from the control plate. The movable portion is disposed adjacent the control plate within an area defined by the arcuate portions. At least one of the arcuate portions has an inwardly and transversely extending lip for engaging an edge portion of the movable switch portion to prevent the movable switch portion from being easily removed from the immediate vicinity of the control plate.
A preferred method of making a two compartment motor constructed in accordance with the present invention comprises the steps of: mounting the plurality of control components to the control plate; mounting the stator windings within the frame; rotatably supporting the armature between the end shields and attaching the end shields to the frame such that the frame and the end shields define a first compartment and the stator windings and armature are disposed within the first compartment; mounting the control plate adjacent one of the end shields and electrically connecting one or more of the plurality of components to the stator windings; and mounting the cover adjacent the control plate and end shield to define the second compartment which encloses the control plate and components. The method may include the additional step of forming the control plate with integral means for mounting at least one of the plurality of control components to the control plate. Additional steps may include interconnecting the plurality of control components with a plurality of electrical conductors, terminating one or more of the conductors in a first electrical connector, connecting the stator windings to a second electrical connector, and matingly connecting the first and second electrical connectors. The control plate may be specially formed for receiving the mated first and second connectors to secure the connectors in position between the end plate and the control plate. The forming step may also include forming at least a portion of a voltage or speed control switch integrally with the control plate. An additional step may involve mounting a rotatable portion of a centrifugal switch on a shaft of the armature between the control plate and the adjacent end shield. In this case, the forming step may additionally comprise forming the control plate to include means for mounting a stationary portion of the centrifugal switch to the control plate.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.